The invention relates to an electrically heated steam iron comprising a soleplate in which are arranged an electrical heating element and a vaporization chamber, and a soleplate liner made of a different material from the soleplate and secured to the underside thereof.
Soleplates for electrically heated steam irons are generally made from a single material, preferably aluminum or steel. Aluminum soleplates are intrinsically lightweight and have good heat conducting properties while having poor resistance to abrasion, while steel soleplates are heavy and have poor heat conducting properties but are highly resistant to abrasion. In order to make use of the advantages and disadvantages of both types of material, it is known to file a thin-walled steel soleplate liner to an electrically heated aluminum soleplate (German Gebrauchsmuster No. 19 39 634). As is well known, steel and aluminum have different coefficients of expansion. When temperature variations occur, as a result of the different coefficients of expansion of steel and aluminum, tensions are produced between the thin-walled steel soleplate liner and the electrically heated aluminum soleplate which stresses the material. Such stresses may exceed the elastic limit of the soleplate and liner materials, possibly causing deformation particularly of those parts of the steel soleplate liner in which steam distribution grooves run at right angles to the direction of expansion.
The center of gravity of the surface is the central starting point for the thermally produced stresses, and the stresses run in straight lines from this point outwardly. The center of gravity of the surface does not change its position. Plastic deformation occurs in the steel soleplate liner, particularly in the region of the steam distribution grooves, and this deformation is not reversed as the temperature changes but remains visible. Such deformation not only makes a steam iron of this kind visually unattractive but also renders the steam iron technically unusable since the finished appearance of fabric ironed with an iron deformed in this way is very poor. Furthermore, the deformation of the steel soleplate liner may cause cracking to a greater or lesser extent in the steel soleplate liner, which will damage the fabric during ironing.